Chop rosemary and set aside.

Chop shallot and set aside.

Cut off and discard the rind from the brie, then cut cheese into small cubes. Set aside.

Melt the butter in a large skillet with deep sides over medium heat. Add the shallots and stir to coat with the butter. Let sauté 2-3 minutes, until softened, then add the mushrooms. Stir to coat and let cook 2-3 minutes, until slightly softened, then add the sherry to the pan.

Let mushrooms and shallots cook in the pan another 3-4 minutes until mushrooms fully softened and shallots are browned.

Add the 3/4 cup of chicken broth slowly to the mixture, using your spatula to de-glaze the pan.

Add milk, uncooked pasta, Worcestershire sauce, ground mustard, and nutmeg. Stir to combine, making sure that the pasta is completely covered by the liquid in the pan. If it’s not, add just enough chicken broth to cover the pasta.

Simmer on medium for 10-15 minutes, stirring regularly, until pasta has absorbed most of the liquid and is cooked to al dente. (If liquid is almost absorbed but pasta is not cooked, add a little more broth to the pan.)

Turn heat to low and add the brie cubes to the pan. Stir constantly until brie is melted and thoroughly coats the noodles. Stir in 2 tsp chopped rosemary, then add salt and pepper to taste.

Remove pan from heat and serve immediately with additional rosemary as garnish.